The present invention relates to a fluid-pressure driving device suitable for actuating a device such as a circuit breaker requiring a high speed operation and high response characteristics.
As is well known, high operation speed is an important requisite for circuit breakers. The current trend for greater electric power supply and larger transmission capacity has given a rise to the demand for circuit breakers having greater capacities and operable at higher voltages. On the other hand, there is a demand for higher transient stability in the electric power transmission system. In view of the above, it is highly desirable to attain a higher interrupting speed, i.e., a shorter breaking time. The shortening of the breaking time will be achieved mainly through a shortening of the arcing time and an increase in the operation speed of an actuator which separate the contactors of the circuit breaker.
In for example, U.S. Pat. No. 4,289,063 a fluid-pressure driving is proposed which includes a fluid-pressure driving device unit and a control valve for controlling this unit. Needless to say, a circuit breaker having a large capacity employs a movable part of a large mass which, in turn, requires a large actuating power when quickly accelerated because of a larger inertial force. Consequently, the size and power of the actuator has to be increased correspondingly. The greater capacity of the fluid-pressure driving device inevitably requires a large flow rate of the working fluid, particularly when it is required to operate at a high speed. Consequently, the size and weight of the movable part in the control valve of the device are increased to exhibit a greater inertial force, resulting in a delay of response to the operating instruction. This known fluid-pressure driving device, therefore, is still unsatisfactory from the view points of operation speed and response characteristics.
It is to be pointed out also that the fluid-pressure driving device requires a large displacement or volume of fluid moved in each operation cycle, necessitating a pressurized fluid source of a large capacity.